Conventional printing ink and coating compositions have been formulated to contain water based acrylic and/or polyamide polymers as a pigment binder. For example, U.S. Pat. No. 5,948,419 discloses the use of aqueous emulsion acrylic polymers to formulate nail coatings. To improve the hardness and adhesion performance properties of such nail coatings, the acrylic emulsion is reacted with an organofunctional hydrolyzable silane coupling agent. In another example, U.S. Pat. No. 6,620,880 discloses architectural coatings wherein an improvement in water resistance is achieved by employing coating formulas containing a starch which has been modified by having an acrylic monomer grafted onto it.
Where conventional formulas containing acrylic polymer and/or co-polymer as the pigment binders are used as printing inks and coatings, these formulas typically suffer from a loss in gloss, wet block resistance, shelf life viscosity stability and pH stability. Another disadvantage for ink and coating formulas using acrylic polymers and co-polymers as a pigment binder is that they require the incorporation of an excess of amine in order to maintain the solubility of the acrylate and stabilize the viscosity and pH of the formula. In addition, the unavoidable evaporative losses of amine, can inherently contribute to a pH drift in the formulation, generating odor. Ink formulas using water based polyamide polymers and co-polymers as the pigment binder exhibit similar disadvantages such as the poor repulpability of substrates or materials printed with such ink and higher initial viscosities.
Starches or polysaccharides have been used to formulate water based newsprint inks. For example, U.S. Pat. No. 4,310,356 discloses an aqueous newsprint ink formula containing carbon black pigment, a starch such as corn starch, corn dextrin or potato dextrin and a salt such as calcium chloride, which acts as a viscosity stabilizer. In such ink formula, the salt is employed to offset the viscosity increase over time caused by the starch via a process called “retrogradation” whereby the starch molecules form intermolecular associations. As such, the viscosity of the ink will depend mainly on the amount and type of starch used in the ink formula. In addition, the starch may be cross-linked by cross-linking agents such as urea-formaldehyde, ketone, resorcinol-formaldehyde, melamine-formaldehyde, glyoxals and carbamates to improve the water resistance of the ink. In another example, U.S. Pat. No. 4,310,356 discloses a water based news print ink prepared using pigment and starch. The inks, however, are not fully suitable for printing on corrugated substrates owing to their poor drying, rub resistance, hiding power and foaming properties.
It is an object of the present invention to provide printing ink and coating compositions designed to print on towel, tissue, corrugated substrates and other porous substrates, offering improvements in chemical resistance, solubility, ink strength, pigment loading, pH stability, higher coefficient of friction, and heat resistance. Such printing ink compositions would also offer improved repulpability of substrates or materials printed with such compositions. Another object of the present invention is to eliminate the need for incorporating excess amine in acrylic based formulas to solubilize the acrylate and thus reduce any odor otherwise generated by such amines.